" my grandfather, Dock Harper, worked as a riding boss and was the last man to leave Mr. Wright when the plantation was lost in the early 20's."

Which "Wright Plantation" are you taking about? There were two.

The Wright plantation at Pastoria, and the lessor known Wright plantation at Pine Bluff. It is the Wright Plantation at Pine Bluff, 4 mile north of the Pine Bluff Courthouse, that was the site of Walkers Division "Camp Wright".